1. Field of the Invention
The invention relates to a device for delivering a reducing agent, in particular a mixture of urea and water, to an exhaust system of an internal combustion engine.
In selective catalytic reduction or SCR, to reduce the proportion of nitrogen oxide in the exhaust gas from diesel engines, a mixture of urea and water, commonly also called AdBlue, is delivered to the exhaust system. The urea in the injected solution is converted in the exhaust system into ammonia (NH3), which in a downstream SCR catalytic converter converts the nitrogen oxides (NOx) contained in the exhaust gas, forming molecular nitrogen (N2) and water (H2O). Since in this way the nitrogen oxides (NOx) can be removed almost completely from the exhaust gas, diesel engines can be operated with a relatively lean mixture, which in turn makes fuel-saving operation of the engines possible. The use of other reducing agents, however, is also conceivable.
2. Prior Art
In known devices of the type defined at the outset, with which a mixture of urea and water is delivered as a reducing agent to the exhaust system, the deliver is effected either by means of a feed pump without a quantity-metering function, or by means of a metering pump. The feed pumps mentioned first have the advantage over metering pumps that they are not only chemically resistant to the urea or free ammonia in the mixture of urea and water, but if the mixture of urea and water freezes, they can also withstand the ice pressure resulting from its increase in volume without being damaged, which is not assured in the metering pumps mentioned second.